In many legacy telecommunications networks, nodes in the network communicate using time-division multiplexing (TDM). TDM combines multiple data streams into one signal, thereby allowing the data streams to share physical lines in the data path without interfering with one another. More specifically, as its name suggests, TDM divides the signal into a number of segments, each constituting a fixed length of time. Because the sending node assigns data to the segments in a rotating, repeating sequence, the receiving node may reliably separate the data streams at the other end of the transmission medium.
With the rapid development of modern packet-switched networks, however, TDM has gradually fallen out of favor as a preferred technology. For example, Voice-Over-Internet Protocol (VoIP) services have replaced many TDM-based services, given VoIP's flexibility, ease of implementation, and reduction in costs. Unfortunately, transitioning to IP-based services requires a service provider to incur significant expenses in expanding its infrastructure and replacing customer premise equipment.
Given the large initial investment, many service providers have been reluctant to switch from TDM-based services to corresponding services in packet-switched networks. TDM pseudowires allow service providers to gradually transition to packet-switched networks, eliminating the need to replace TDM-based equipment and drop support of legacy services. In particular, on the ingress end of a TDM pseudowire, a node converts the TDM signals into a number of packets, then sends the packets across a packet-based path, or pseudowire. Upon receipt of the packets, a node on the egress end converts the packets back into TDM signals and forwards the TDM signals towards their ultimate destination.
As with any network service, service providers invest significant amounts of time and money in maintaining reliable connections for TDM pseudowire services. In the event of outages, service providers strive to restore connectivity to the customer as quickly as possible.
Unfortunately, fast restoration of service is often difficult in TDM pseudowires implemented according to Request for Comments (RFC) 4553, “Structure-Agnostic Time Division Multiplexing over Packet (SAToP),” published by the Internet Engineering Task Force and incorporated by reference herein in its entirety. During network delay and loss scenarios, a provider edge node notifies the connected customer edge (CE) device. When the provider edge node operates in accordance with RFC 4553, this notification causes the CE device to determine that the particular port is down. As a result, upon restoration of service, the CE device must first restore Layer 1 connectivity on the port, then restore Layer 2 connectivity, and so on. This process is time consuming, often taking many seconds to properly restore service to the CE device. In the interim, the customer is unable to exchange data between the two TDM endpoints.
In view of the foregoing, it would be desirable to more reliably manage TDM over pseudowire connections during network outages. More specifically, it would be desirable to decrease outage times during packet loss and delay situations in TDM pseudowires implemented according to a structure-agnostic transmission mechanism, such as SAToP. Other desirable aspects will be apparent to those of skill in the art upon reading and understanding the present specification.